Day 21 solutions

21/21-1.c

@@ -0,0 +1,71 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include "../check_alloc.h"
+
+#define P1_START 4
+#define P2_START 8
+
+#define MIN(x, y) ((x) < (y) ? (x) : (y))
+
+typedef struct
+{
+    int position;
+    int score;
+} PLAYER;
+
+PLAYER *new_player(int initial_position)
+{
+    PLAYER *p_player = calloc(1, sizeof(PLAYER));
+    CHECK_ALLOC(p_player);
+    p_player->position = initial_position;
+    return p_player;
+}
+
+void move_position(PLAYER *player, int move)
+{
+    int next_pos = (player->position + move) % 10;
+    player->position = next_pos == 0 ? 10 : next_pos;
+    player->score += player->position;
+}
+
+typedef struct
+{
+    int value;
+    int rolls;
+} DICE;
+
+#define NEW_DICE() calloc(1, sizeof(DICE))
+
+int roll_dice(DICE *dice)
+{
+    dice->value = dice->value % 100 + 1;
+    dice->rolls++;
+    return dice->value;
+}
+int roll_3(DICE *dice)
+{
+    int value = roll_dice(dice);
+    value += roll_dice(dice);
+    value += roll_dice(dice);
+    return value;
+}
+
+int main(int argc, char const *argv[])
+{
+    DICE *p_dice = NEW_DICE();
+    PLAYER *p_p1 = new_player(P1_START);
+    PLAYER *p_p2 = new_player(P2_START);
+    while (1)
+    {
+        int value = roll_3(p_dice);
+        move_position(p_p1, value);
+        if (p_p1->score >= 1000)
+            break;
+        value = roll_3(p_dice);
+        move_position(p_p2, value);
+        if (p_p2->score >= 1000)
+            break;
+    }
+    printf("END RESULT %d\n", p_dice->rolls * MIN(p_p1->score, p_p2->score));
+    return 0;
+}

21/21-2.c

@@ -0,0 +1,87 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+
+// I needed some help for this one. Couldn't be bothered to implement a cache etc.
+// I calculated the DICE array, but struggled getting the total wins. Instead of
+// multiplying as I went up, I tried to multiply when a result occurred but
+// obviously this was the wrong way to think about it.
+
+#define P1_START 6
+#define P2_START 1
+
+typedef struct
+{
+    int position;
+    int score;
+} PLAYER;
+
+PLAYER clone_player(PLAYER player)
+{
+    PLAYER new_player = {player.position, player.score};
+    return new_player;
+}
+
+void move_position(PLAYER *player, int move)
+{
+    int next_pos = (player->position + move) % 10;
+    player->position = next_pos == 0 ? 10 : next_pos;
+    player->score += player->position;
+}
+
+typedef unsigned long long NUMBER;
+
+typedef enum
+{
+    P1,
+    P2
+} TURN;
+
+typedef struct
+{
+    NUMBER p1_wins;
+    NUMBER p2_wins;
+} SCORE;
+
+// PRE-CALCULATED OCCURRENCES OF TOTALS FOR ROLLING 3 DICE
+int DICE[] = {1, 3, 6, 7, 6, 3, 1};
+
+// repeat TRACKS THE AMOUNT OF POSSIBLE COMBINATIONS LEADING TO A WIN,
+// THIS REDUCES THE SEARCH AREA GREATLY BY IGNORING PATHS TO THE SAME WIN.
+void iter_rolls(PLAYER p1, PLAYER p2, TURN turn, NUMBER repeat, SCORE *score)
+{
+    for (int i = 0; i < 7; i++)
+    {
+        int value = i + 3;
+        PLAYER tmp;
+        if (turn == P1)
+            tmp = clone_player(p1);
+        else
+            tmp = clone_player(p2);
+        move_position(&tmp, value);
+        if (tmp.score < 21)
+        {
+            if (turn == P1)
+                iter_rolls(tmp, p2, P2, repeat * DICE[i], score);
+            else
+                iter_rolls(p1, tmp, P1, repeat * DICE[i], score);
+        }
+        else
+        {
+            if (turn == P1)
+                score->p1_wins += repeat * DICE[i];
+            else
+                score->p2_wins += repeat * DICE[i];
+        }
+    }
+}
+
+int main(int argc, char const *argv[])
+{
+    PLAYER p1 = {P1_START, 0};
+    PLAYER p2 = {P2_START, 0};
+    SCORE *p_score = malloc(sizeof(SCORE));
+    iter_rolls(p1, p2, P1, 1, p_score);
+    printf("WINNER SCORE %llu\n", p_score->p1_wins > p_score->p2_wins ? p_score->p1_wins : p_score->p2_wins);
+    return 0;
+}